After all, Marcus had been an entrepreneur all his life. He had never managed more than 250 people. PayPal employed 13,000. He didn't need corporate headaches. Nor did he need a paycheck--he had sold his mobile payment company, Zong, to PayPal parent for $240 million in 2011.

At PayPal Marcus began what he called an "invisible turn around"--reinvigorating PayPal while growth was still humming. PayPal had been notoriously bureaucratic and sluggish. Marcus cut the fat. He blew apart its nine-silo system and adopted a single, more adaptable set of software tools.Next he recruited serious tech talent from Netflix, Google, Amazon and Box, while laying off about a third of the engineering team. Most importantly he PayPal’s culture to its roots, buying $1 billion worth of start-ups and stacking the division’s top ranks with career entrepreneurs.

It was exhausting. As he told me this winter: “It’s a 13,000-person company where we’re changing everything and rewiring the whole culture... It’s really brutal... At large companies you always find someone with reasons not to do something–the self-preservation thing is highly frustrating.”

It now appears running PayPal grew too frustrating for Marcus to bear. He's left PayPal to run Facebook Messenger. Today in public Facebook post, Marcus echoed what he had told FORBES this January writing:

Going from managing a few hundred people at best in my entrepreneurial career, I suddenly found myself leading 14,000. The first year took its toll on me. It was hard. The second year started becoming more “natural”, and as we made progress on a number of fronts: technology, product, marketing, sales, and more importantly culture. I realized that my role was becoming a real management one, vs. my passion of building products that hopefully matter to a lot of people. So after much deliberation, I decided now is the right time for me to move on to something that is closer to what I love to do every day.